Carbon-carbon composites are tough, strong, lightweight materials that are useful as structural material in applications where strength to weight ratio is important. Carbon-carbon composites incorporate graphite fibers in a carbon matrix so as to reinforce the matrix and may be formed, for example, by impregnating graphite cloth wtth a resinous material, layering plies of the resin-impregnated graphite cloth and then carbonizing the resin-impregnated layered plies with the application of heat and pressure.
An important limitation to the use of carbon-carbon composites is the fact that they are quite susceptible to oxidation in high-temperature, oxidizing environments. Oxygen not only attacks the surface of carbon-carbon composite but seeps into the pores that invariably are present, oxidizing the surfaces of the pores and continuously weakening the composite. If carbon-carbon composites could be rendered resistant to oxidation at high temperatures, e.g., above about 500.degree. C., and still retain their desirable thermal and mechanical properties, their usefulness would be significantly enhanced, e.g., in systems, such as heat engines and rockets, where high strength, lightweight, oxidation-resistant components are required to operate for long time periods under high stresses generated by thermal cycling. Accordingly, it is a general object of the present invention to provide carbon-carbon composites that have improved resistance to oxidation.